1. FIELD OF THE INVENTION
This invention relates in general to the construction of rocket engine combustion chambers and, in particular, to a new and useful rocket engine which operates with non-hypergolic propellant components and to an ignition system therefor.
2. DESCRIPTION OF THE PRIOR ART
In a known ignition system for combustion chambers of rocket engines operated by non-hypergolic propellants, such as liquid hydrogen and liquid oxygen, a liquid, for example, aluminumtriethyl is used as the igniting agent, which is self-reacting with the liquid oxygen. The substantial parts of this ignition system are as follows:
A. AN IGNITION CONDUIT LEADING INTO THE COMBUSTION CHAMBER IN THE ZONE OF THE INJECTION SYSTEM FOR BOTH OF THE PROPELLANT COMPONENTS;
B. A TWO-WAY REVERSING VALVE; AND
C. A CYLINDER-PISTON UNIT.
The piston of the cylinder-piston unit divides the interior of the cylinder into two spaces. One space is the pressure space for the working fluid or propellant component. If necessary, the working fluid is supplied from the hydrogen storage tank, hydrogen being the propellant component, non-hypergolic with the igniting agent, i.e., the aluminumtriethyl. The other cylinder space is used as a storage space for the igniting agent. In this space, a quantity of aluminumtriethyl is stored which is sufficient for several ignitions, and the space communicates with the ignition conduit through an outlet bore. The outlet bore is controlled by a two-way reversing valve. In its position of normal operation of the combustion chamber, the two-way valve closes the outlet bore for the igniting agent and simultaneously opens a scavenging circuit comprising the ignition conduit. In its position for ignition, the two-way valve opens the outlet bore for the igniting agent and closes the scavenging circuit. A certain portion of hydrogen, i.e., of the propellant component non-hypergolic with aluminumtriethyl and which already serves as the working fluid, is also used as the scavenging fluid.
In the ignition system just described, the piston ensures a spacial separation of the igniting agent (aluminumtriethyl) from the working fluid (hydrogen) which latter is responsible for the injection of the agent into the combustion chamber. The piston thus prevents, with certainty, the mixing of the two substances below the ignition limit. On the other hand, as already mentioned, the aluminumtriethyl is injected into the combustion chamber through a single conduit. However, with such a localization of the ignition focus, a spontaneous initiation of the combustion in the chamber is not always assured and misfiring is not excluded. In addition, in the intermediate time between the ignition phase and full operation of the combustion chamber, i.e., at the end of the ignition phase, both aluminumtriethyl and hydrogen pass into the combustion chamber in the zone of the ignition conduit as a mixture. During the subsequent combustion of this mixture with oxygen, high temperature peaks occur which may result in overheating and damage of the walls of the combustion chamber. To avoid such consequences, efforts are made to minimize the quantity of the igniting agent to be injected. Such a measure, however, requires narrow ignition conduits which may again become a source of ignition troubles because of their susceptibility to carbonization.
For the foregoing reasons, another known ignition system of the mentioned type has dispensed with the storage of a quantity of aluminumtriethyl sufficient for several combustion chamber ignitions and with the supply by portions of this igniting agent from the storage space through a separate conduit into the combustion chamber. Instead, a predetermined quantity of aluminumtriethyl for a single ignition is stored in an appropriately dimensioned storage space and, at the required moment, is transferred into the combustion chamber through the injection bores provided for and by the action of the propellant component which is non-hypergolic with the aluminumtriethyl, for example, hydrogen. A spontaneous initiation of the combustion over the entire cross-sectional area of the chamber is thereby reliably obtained and no additional expenditures of equipment, accessories, or structural adaptation are incurred because of the utilization of the existing equipment for the propellant supply and ignition; that is, the igniting agent (aluminumtriethyl) is driven into the combustion chamber by the propellant component (hydrogen) which is non-hypergolic therewith and which, after the ignition, takes over the full scale operation in the combustion chamber along with the other propellant component (oxygen), in a "seamless" transition. A hollow cylinder is again provided as the storage space for the igniting agent. This space, however, is connected to the propellant supply conduit leading from the hydrogen storage tank to the injection head of the combustion chamber. The aluminumtriethyl is stored in the cylinder between two metallic burst diaphragms. The two burst diaphragms are destroyed as soon as they are exposed to the pressure under which the hydrogen is stored. The diaphragm destruction immediately preceding the transfer of the igniting agent into the combustion chamber is harmless in cases where non-aggressive igniting agents are used, among which the mentioned aluminumtriethyl is numbered. The conditions change completely, however, if fluorine or a similar aggressive fluid distinguished by its spontaneous hypergolic reactivity with hydrogen should be uased as the igniting agent. As is well known, igniting agents of such a kind require a passivation of the metals with which they come into contact. Without passivation, destruction of the burst diaphragms would have serious consequence because a sudden inflammation of the rupture areas would follow. Still another risk is involved in the destruction of the diaphragms, namely, the possibility of a subsequent mixing of the igniting agent and the pushing propellant component in a proportion below the ignition limit. This risk is particularly great in cases where the densities of the igniting agent and of the propellant component transferring it into the combustion chamber of the rocket are equal to each other or only slightly different.